src/node_device/node_device_udev.c was using a function available only
on the daemon code, fix this and use the function available globally

* src/node_device/node_device_udev.c: replace use of virEventAddHandleImpl
  by virEventAddHandle

Provides the CDROM label for current media. Only implemented for the
udev backend.

Replace free(virBufferContentAndReset()) with virBufferFreeAndReset().
Update documentation and replace all remaining calls to free() with
calls to VIR_FREE(). Also add missing calls to virBufferFreeAndReset()
and virReportOOMError() in OOM error cases.

Fix crash on strdup in that case.

I realized that I inadvertently added a member to the def struct to
contain each device's sysfs path when there was an existing member in the
dev struct for "OS specific path to device metadat, eg sysfs"  Since the
udev backend needs to record the sysfs path while it's in the process of
creating the device, before the dev struct gets allocated, I chose to
remove the member from the dev struct.

* src/conf/node_device_conf.c src/conf/node_device_conf.h
  src/node_device/node_device_driver.c src/node_device/node_device_hal.c
  src/node_device/node_device_udev.c: remove devicePath from the
  structure and use def->sysfs_path instead

uses libpciaccess to provide human readable names for PCI vendor and
device IDs
* configure.in: add a requirement for libpciaccess >= 0.10.0
* src/Makefile.am: add the associated compilation flags and link
* src/node_device/node_device_udev.c: lookup the libpciaccess for
  vendor name and product name based on their ids

* src/conf/node_device_conf.h src/conf/node_device_conf.c: add specific
  support for SCSI target in node device capabilities
* src/node_device/node_device_udev.c: add some extra detection code
  when handling udev output

* configure.in: add new --with-udev, disabled by default, and requiring
  libudev > 145
* src/node_device/node_device_udev.c src/node_device/node_device_udev.h:
  the new node device backend
* src/node_device/node_device_linux_sysfs.c: moved node_device_hal_linux.c
  to a better file name
* src/conf/node_device_conf.c src/conf/node_device_conf.h: add a couple
  of fields in node device definitions, and an API to look them up,
  remove a couple of unused fields from previous patch.
* src/node_device/node_device_driver.c src/node_device/node_device_driver.h:
  plug the new driver
* po/POTFILES.in src/Makefile.am src/libvirt_private.syms: add the new
  files and symbols
* src/util/util.h src/util/util.c: add a new convenience macro
  virBuildPath and virBuildPathInternal() function